Lubrication of controlled-slip differential

ABSTRACT

1. IN THE ART OF LUBRICATION OF A CONTROLLED-SLIP DIFFERENTIAL WHICH HAS STARTED TO SLIP EXTENSIVELY DUE TO SUBSTANTIAL WEAR, THE IMPROVEMENT WHEREIN THE PREVIOUSLY USED LUBRICANT IS REPLACED BY A LUBRICANT CONSISTING ESSENTIALLY OF NON-HYDROCARBON ADDITIVES AND A HYDROCARBON BASE STOCK HAVING A KINEMATIC VISCOSITY AT 210*F. IN THE RANGE OF 1.5-200.0 CS. AND CONSISTING ESSENTIALLY OF A BLEND OF AT LEAST ONE C13-C29 NAPHTNENE AND FROM 0.1-20 PARTS BY WEIGHT, BASED ON SAID NAPHTHENE OF AT LEAST ONE MEMBER FROM AT LEAST ONE OF THE FOLLOWING GROUPS (A) AND (B): (A) A SYNTGETIC LIQUID C3-C8 OLEFIN HOMOPOLYMER; AND (B) A MEMBER FROM GROUP (A) ABOVE WHICH IS AT LEAST PARTIALLY HYDROGENATED; AND WHEREIN THE AMOUNT OF SAID BLEND WHICH IS PRESENT IN SAID BASE STOCK IS SUFFICIENT TO PROVIDE A GREATER COEFFICIENT OF TRACTION, MEASURED AT 600 FT./MIN., 200*F., 400,000 P.S.I., THAN WOULD BE PROVIDED BY SUBSTITUTION OF THE SAME AMOUNT OF ASTM OIL NO. 3 FOR SAID BLEND IN SAID BASE STOCK.

Oct. 22, 1974 GATES ETAL 3,843,534

LUBRICATION 0F CONTROLLED-SLIP DIFFERENTIAL Filed Feb. 19, 1971 CONTROLLED-SLIP DIFFERENTIAL l'llllll United States Patent cc 37843534 Patented Oct. 22, 1974.-

The disclosure of all of the above-cited applications is 3,843,534 hereby incorporated herein (by this reference). In par- LUBRICATION 0F N R ED- P ticular, these applications disclose blended lubricants DIFFERENTIAL which are useful in the present invention, additives which David Gates swarthmore Paul Hagstmm Valley can be useful in such lubricants and processes for mak- Forge, and Marcus W. Haseltine, Brookhaven, Pa,

assignors to sun Oil Company of Pennsylvania, Phila ing individual components of such belnds. delphia, P a. BACKGROUND OF THE INVENTION fggg i' if i gg' 22 As has been reported by R. L. Kostelak in Lubrication mg C], 252 45 15 Cl i Vol. 56, #4, 1970 (p. 49 et seq.), the principle of operation of the conventional diiferential in todays American ABSTRACT 05' THE L SU automobile remains the same as the Pecqueur differential,

invented in 1827. Although this conventional diflerential generally performs very satisfactorily, it has one serious shortcoming; namely, stalling, which occurs when either rear wheel loses traction. Due to the kinematics of the conventional differential design, the driving torque is divided equally between the two rear wheels and is limted by the wheel with the least traction. Hence,

An approved method of lubrication of a controlledslip diflerential comprises using a lubricant comprising a hydrocarbon base stock having a kinematic viscosity at 210 F. in the range of 1.5-200.0 es. and containing a blend of at least one (Z -C naphthene and from 0.1- parts by weight, based on said naphthene of at least one member from at least one of the following groups when one wheel loses traction, the vehicle does not move. (a), (b), (c) and (d): 20 To prevent this shortcoming, engineers have developed (a) a synthetic liquid C -C olefin homopolymer copolymany ingenious ideas and mechanisms. Each manumer, or terpolymer; facturer has his own descriptive name for his particular (b) a member from group (a) above which is at least mechanism; for example, Chevrolet Positraction, Chrysler partially hydrogenated; Sure-Grip, and Ford Traction-Lok. Generally, however, (c) a severely hydrorefined naphthenic lube containing a differential incorporating one of these mechanisms is less than 1% of gel aromatic hydrocarbons; and called a locking or limited slip or controlled-slip (d) a severely hydrorefined parafiinic lube containing differentialless than 1% of gel aromatic hydrocarbons; The limited slip diifefiential used in the American and wherein the amount of said blend which is present passage}. car is essentm t 6 m as a conventlonal in Said base Stock is Sufiicient to provide a greater differential except for the incorporation of some form of a friction members (e.g. clutch plates or friction cones). gz i 3232i; ggg i i g gi g gg gg The Kostelak article describes the conventional differof the sage amount of ASTM 8.1 No 3 tin said blend and typlc-al differ-611mb in said base stock. The preferred lubricant also contains g g f i fg i 16 Lubnc-ants for Llmlted an extreme pressure additive (e.g. tricresyl phosphate) g I i fi f giver} at Fue.1s and and an additive which lowers the static friction of the u mean S ee Oclety O Automotlve Engmeers Houston, Texas, Nov. 1-3, 1966. lubricant (e.g. a surface-active, organic phosphate ester of a linear aliphatic, ethoxylated alcohol). SUMMARY OF THE INVENTION In a combination of a controlled-slip difierential and CROSS RELATED a lubricant therefor, we have discovered an improvement wherein said lubricant comprises a hydrocarbon base The present application is related to the following stock having a kinematic viscosity at 210 F. in the range listed applications: a of 1.5200.0 cs. and contains a blend of at least one Serial No. Filing date Title/inventor(s) 621,443- 3-8-67 (now Synthetic Lubricants From Low Molecular Weight OlefinsRichard S. Stearns,

(siban) Irl N. Duling and David S. Gates.

one 679,801 (now U.S. 3,597,358 issued 8-3-71) 11- -67 Traction Drive Transmission Containing Adamantane Compounds as Lubricant Irl N. Duling, Frederick P. Glazier, David S. Gates and Robert E. Moore. 679, 833 (new U.S.3,595,796 issued 7-27-71) 11-1-67 Traction Drive Transmission Containing Naphthenes, Branched Paraifins, or 1lglentssot(13:1aglhiilloi'ies and Branched Paraflins as Lubricant-Irl N. Duling and avi a es. 679,834 (now 11.8. 3,595,797 issued 7-27-71) 11-1-67 Blending Branched Paraffin Fluids for Use in Traction Drive Trausmissi0nIrl N.

Duling, David S. Gates and Marcus W. Haseltine. 679,851 (now U.S. 3,598,740 issued 8-10-71) 11-1-67 Traction Drive Transmission Containing Paralfinic Oil as LubricantIrl N.

Duling, David S. Gates and Thomas D. Newingham. 784,487 (now US. 3,646,224 issued 2-29-72) 12-17-68 Conversion of Adamantane Hydrocarbons to MonoolsRobert E. Moore. 794,844 (now U.S. 3,608,385 issued 928-71) 1-24-69 Friction Drive Fluid-Irl N. Duling and F ederi k P, Gl i 812,516 (now 11.8. 3,619,414 issued 11-9-71) 2-19-69 Catalytic Hydrofinishing of Petroleum Distillates in the Lubricating Oil Boiling RangeIvor W. Mills, Merritt C. Kirk, J r. and Albert '1. Olenzak. 823,138 (now US. 3,560,518 issued 2-2-71) 5-8-69 Reaction for Linking Nuclei of Adamantane HydrocarbonsAbraham Schneider. 850,717 8-18-69 (now Hydrorefi d Lu e il a d Process of Manufacture-Ivor W. Mills and Glenn aban- R. Dimeler. doned). I I 876,993 (now U.S. 3,645,902 issued 2-29-72) 11-14-69 Friction on Tractive Drive Fluid Comprising Adamantanes-Irl N. Duling,

Frederick P. Glazier, David S. Gates and Robert E. Moore. 877,462 11-17-69 (new Combination of Traction Drive and Traction Fluid Comprising Saturated Cyclic gbant-i) Compounds1rl N. Duling and Frederick P. Glazier.

one 3,256 (now US. 3,648,531 issued 3-14-72) 8-19-69 Frictio o Tractive Drive u.id-Irl N. Duling, Frederick P. Glazier, David S.

Gates and Robert E. Moore. 28,942 4-15-70 Prlgcess 1ilor Producing Polyisobutylene Oil-Alfred E. Hirschler and Gary L. risco 33,023 4-29-70 (now Combination of Tractive Drive and Traction Fluid Comprising Cyclic or Acyclic gban) Compounds-Irl N. Duling and Frederick P. Glazier.

one 52,301- 7-6-70 Polyisobutylene Oil Having a High Viscosity Index-Gary L. Driscoll, Irl N.

Duling and David S. Gates. 78,190 (new US. 3,737,477 issued 6-5-73) 10-5-70 Process of Preparing Synth tic Lu ricants From Low Molecular Olefins Richard S. Stearns, Irl N. Duling and David S. Gates. 78,191 (now US. 3,676,521 issued 7-11-72) 10-5-70 Synthetic Lubricants From Low Molecular Weight Olefil1S-RiCl1aId S. Stearus,

Irl N. Duling and David S. Gates. 86,779 (new US. 3,646,233 issued 2-29-72) 10-14-70 Reaction of Normal Paraifins With Adamantaue Compounds-Robert E. Moore.

C -C naphthene and from 0.120 parts by weight, based on said naphthene, of at least one member from at least one of the following groups (a), (b), (c) and (d):

(a) a synthetic liquid C -C olefin homopolymer copolymet, or terpolyrner;

(b) a member from group (a) above Which is at least partially hydrogenated (preferably, to an iodine number less than 20, more preferably less than and/or having a 195 UVA less than 2.0);

(c) a severely hydrorefined naphthenic lube containing less than 1% of gel aromatic hydrocarbons; and

(d) a severely hydrorefined paraffinic lube containing less than 1% of gel aromatic hydrocarbons;

and wherein the amount of said blend which is; present in said base stock is sufiicient to provide a greater coeflicient traction, measured at 600 ft./min., 200 R, 400,000 p.s.i., than would be provided by substitution of the same amount of ASTM Oil No. 3 for said blend in said base stock. The preferred lubricant has a viscosity in the range of 5-50 cs. at 210 F., (typically -20 cs), has. a channel point below 32 F. (more preferred below 10 F., typically 0 to F.) and also contains an extreme pressure (EP) additive (e.g. tricresyl phosphate, zinc dithiophosphate, etc.) and an additive which lowers the static friction of the lubricant (e.g. a surface-active, or ganic phosphate ester of a linear aliphatic, ethoxylated alcohol).

Preferably, the C -C naphthene has a glass transition temperature in the range of 90 to 30 C. and contains as a structural nucleus, a cyclohexyl hydrindan, di(cycloheyxl) alkane, adamantane, spirodecane, spiropentane, perhydrofluorene, perhydrobiphenyl, perhydroterphenyl, decaline, norbornane, perhydroindacene, perhydrohomotetraphthene, perhydroacenaphthene, perhydrophenanthrene, perhydrocrysene, perhydroindane 1 spirocyclohexane, perhydrocarylophyllene, pinane, camphane, perhydrophenylnaphthalene or perhydropyrene.

These blended hydrocarbon base stocks are described in the aforementioned applications of Duling et al. {c.g. see Ser. No. 33,023, filed Apr. 29, 1970) and in the application of Driscoll et al.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is an illustration of a controlled-slip differential and will be referred to with reference to a test method for comparing the dynamic torque obtained from a given combination of lubricant and controlled-slip differential. The test can be useful in comparing various lubricants in a given differential.

For example, in a limited slip differential (LSD), the contact plates can be surfaced with swirl patterns to produce high friction. When the plate has become worn, the friction drops drastically and the LSD fails to perform any better than a conventional differential. With a high traction-LSD fluid, the friction property is inherent in the fluid itself and is not completely dependent on the patterned contact surfaces. Thus, the lubricated contacts can have high friction (or traction) even when badly worn.

With reference to the Figure, torque measurements are made by attaching a belt 10 around one of the rear wheels 8 and connecting the belt end to a calibrated spring scale 11. The other rear wheel 1 is then turned by hand to slip the diiferential. The measurement when slip begins is taken as the break-free torque. A second measurement is determined at approximately r.p.m. (with the wheel 1 being driven by a motor).

The differential in the Figure consists of a ring gear a differential pinion 6 and cross shaft, and a right 7 and a left 2 clutch plate attached to the differential case. The wheels are connected to the differential pinion by the right 5 and left 3 side gears. Clutch plates are also attached to the left and right axle shafts. The differential assembly and the lubricant are contained in a housing 9.

4 EXAMPLE I 466 g. of a commercial a-methyl styrene polymer, obtained by conventional acid-catalyzed polymerization, is placed in a one-liter round bottomed flask, attached to a one-inch column, and dry-distilled with essentially no reflux or fractionation at a pot temperature of about 290 C., and a vapor temperature of about 210 C. under a vacuum of about 6 millimeters of mercury. 373 g. of distillate are obtained and about 73 grams of material remain in the bottom of the flask at the end of the distillation. The commercial ot-methyl styrene polymer has a softening point of 210 F., a Gardner-Holdt viscosity of JL, a specific gravity of 1.075, a refractive index at 20 C. of 1.61, a molecular weight of 685, an iodine number of 0, an acid number of 0, and a saponification number of 0.

EXAMPLE II 300 g. of the distillation product of Example I is placed in a 316 stainless steel bomb along with 7.5 grams of Raney nickel catalyst and the bomb is pressured to 3000 p.s.i.g. of 100% hydrogen while heat is applied until the temperature in the bomb is 150 C. At that point an exothermic occurs and heating is discontinued. The temperature is allowed to rise to about 220 C. and the hydrogen pressure is maintained at 3000 p.s.i. for 6 hours at which time the bomb is slowly cooled to ambient temperature while maintaining the hydrogen pressure at 3000 psi. in order to avoid dehydrogenation of the hydrogenated product. The resulting perhydrogenated poly (or-methyl styrene) oil is topped to remove components boiling below 125 C. The remaining perhydrogenated naphthene product has a KV21O of 11.07 es. and a KV 100 F. of 327.8 cs. Analysts by nuclear magnetic resonance (NMR) shows the oil of this example to contain about 40% of trimers (mostly hydrindan form), and 60% dimers, mainly 1,1,3- trimethyl-3-cyclohexyl hydrindan.

EXAMPLE III A blend of two commercially available polybutene polymers (i.e. vol. percent Indapol L- and 10% Oronite Special 6) is completely hydrogenated to produce a hydrogenated polybutene oil which analyzes 0.5 mole percent olefin by the ultraviolet absorbence method. The hydrogenation is at 200 C., 2000 psi. of 100% hydrogen for 6 hours using Harshaw NI0104P catalyst. The resulting hydrogenated polyolefin oil has a KV 210 F. of 13.54 es. and a KV 100 of 162.8.

EXAMPLE IV A blended base oil was compounded from 61.0 volumes of the naphthene product of Example If and 33.1 volumes of the hydrogenated polyolefin oil of Example III. Then 5.9 volumes of a commercial limited slip axle additive (Lubrizol Company, Anglamol 99LS) was added to the blend to produce a formulated lubricant. Table 1 describes typical properties of Anglamol 99 LS.

TABLE 1 Specific gravity at 60 F., (156 C.) 1.055 Pounds per gallon at 60 F., U.S 8.79 Pounds per gallon at 60 F., IMP. 10.55 Viscosity at 210 F., (989 C.) SUS 60 Viscosity at 210 F., cSt. 10.2

Weight percent of Typical Sulfur 29.2 Phosphorus 2.0

Similarly, other blended base oils (e.g. comprising synthetic paraffins and naphthenes) and other gear oil additives can be used to formulate such lubricants. Other useful additives are those mentioned by F. G. Rounds, Journal of Chem. and Eng. Data, Vol. 5, No. 4, October 1960, pp. 504-505. Useful blended base oils and additives are disclosed, for example, in previously cited applications Ser. Nos. 33,023 and 52,301.

EXAMPLE V Another useful lubricant for a controlled-slip difierential, and which is also useful for lubrication of a traction drive transmission, comprises a blend of the following (all hydrogenations are to at least 98% saturation):

The use in this lubricant of high and low viscosity fractions of the naphthene and paraflin is an example of dumbell-blending to improve viscosity index.

The Ultraphos l1 additive is a surface-active, organic phosphate ester of a linear aliphatic, ethoxylated alcohol.

The synthetic sulfurized oil is the invention of Alexander D. Recchuite and is the subject of a later filed application Ser. No. 135,466, filed Apr. 19, 1971 (now abandoned) and Ser. No. 220,399, filed J an. 4, 1972. This oil can be used as a replacement for sulfurized sperm oil and can be made by heating sulfur and a blend of from 50-95% lard oil and 50-5% of one or a mixture of C -C acyclic monolefin. For example, weight percent of sulfur was added at 250 F. to 90 weight percent of a blend of 85 volumes of lard oil (No. 1 grade) and volumes Chevron C C ot-olefin. The sulfur-containing mixture was heated to 375 F. and maintained at that temperature, with stirring, for 2 hours, then cooled to 200 F., and, finally, blown with air for 1 hour.

Another procedure for making the synthetic sulfurized oil is to heat the lard oil-olefin blend to about 300 F., add sulfur (e.g 525%) over a 30 minute period (with agitation), then bring the temperature to 335 F., maintain for 2 hours, cool to 200 F. and finally blow with air for 16 hours. This later procedure was used for the synthetic sulfurized oil in the above-listed lubricant.

The channel point of a lubricant is determined by drawing a channel with a spatula in a sample of lubricant, at a given temperature, and finding the maximum temperature where the walls of the channel no longer cave-in.

This application is related to commonly-owned ap- The used, original fill fluid was replaced with a fresh conventional petroleum-based LSD fluid (e.g. solvent refined parafi'inic lube plus Anglamol 99LS). Torque measurements were made periodically for the next 500 miles. For the last 100 miles, a 6 p.s.i. difference in air pressure in the rear tires caused the differential to Slip constantly. It was believed that this tire pressure difference caused the fresh fluid to work into the contact areas. At the end of 500 miles, the conventional fluid was replaced with the blended traction-LSD fiui of Example IV, which had the same viscosity at 100 F. and the same additive system as the petroleum-LSD fluid. After 40 miles of driving with the 6 p.s.i. air pressure differential in the rear tires, the torque measurement at the low speed dynamic conditions was nearly double that observed when the petroleum-LSD fluid was usd. There was little difference in the break-free torque since the static friction is primarily dependent on the additive system. Table 2 presents the test data obtained from this testing.

TABLE 2 [Torque through worn limited slip differential] Torque (lbs.)

The high dynamic friction also helped reduce chatter. With high dynamic friction, static friction can increase to a higher level before chatter will occur. Thus, low static modifying additives are effective for a longer period of time in a high traction-LSD fluid. This results in longer LSD fluid life before chatter occurs.

EXAMPLE VII Conventional petroleum-LSD lubricant and the blended Traction-LSD lubricant of Example IV were compared in four limited slip differentials, by the previously described test method. The results of these tests are summarized in Table 3. The performance of each differential was improved when lubricated by the blended traction- LSD lubricant.

TABLE 3 [Torque through various limited slip differentials] O dometer Torque, lbs. Odometer at torque at fliud Car Fluid test Break-free -40r.p.m. change Chev. 1969 Original 11151 20 10 11151 Petroleum-LSD 11437 22-23 12-14 11437 Traction-LSD 11449 25 1520 11539 20 21-22 Original 12808 22-25 6-9 12808 Petroleum-LSD 13239 20-25 6-7 13239 Chev. 1969 74 20 TIBOEIOIPLSD 1330 20 13762 19 Original 05721 30 Pontiac 1970 Petroleum-LSD... 06578 30-32 Traction-LSD 06823 35 06981 35 Original 18617 90 Ford 1968 PetroleumLSD 19145 80-90 Traction-LSD 19198 75 19244 75 plication Ser. No. 116,985 Lubrication for Controlled- Slip Differential of Newingham et al., filed on the same date as the present application.

EXAMPLE VI A well-worn limited slip differential in a 1965 Buick Skylark (driven over 65,000 miles) was used to compare lubricants, by the previously described method.

Any of the usual gear lube additives can be used in the lubricant-differential combination of the present invention; however, especially beneficial results are obtained when 0.25-10% (based on the base stock) Ultraphos 11 (or less preferred, Ultraphos 12) used as one of the additives. Ultraphos 11 is marketed by Witco Chemical Company and has the following typical properties:

KV210:23.44 cs.

Melting Point= C.

Glass Transition Temperature: 62 C.

Alternatively, Antara LB400 (General Aniline and Film) can be used instead of Ultraphos as a low static modifier. Another useful, multipurpose additive package which is useful in such lubricants is 215% Anglamol 93, which has been previously described and which is a product of Lubrizol Company and comprises a mixture of zinc phosphorodithioate and chlorinated hydrocarbons, a typical analysis being 3% Zn, 3% P, 16.5% Cl and 16.0% S.

The blended fluids and limited slip diiferential lubricants referred to herein, especially that of Example N can be used to increase traction between two rolling elements. When traction fluid is used to lubricate high speed ball bearingsfor an example, the main shaft bearings in a turbine engineit reduces ball skidding. Ball skidding is one of the factors limiting shaft speed. Accordingly, such lubricants can be used for high speed and highly loaded bearings. They can also be used for lubrication of overrunning clutches.

During engagement, there is a sliding motion between the cam or rollers and the races in overrunning clutches. Since wear occurs during the engagement period, a lubricant which reduces engagement time will reduce wear and extend service life. In one test, engagement was reduced from 11 to 2 revolutions simply by replacing the conventional petroleum oil grease with a grease component of a naphthene-parafiin blend similar to that of Example IV. The traction fluid and its grease show the greatest advantage in clutches where load is high enough to elasticity deform the rollers or cams.

The invention claimed is:

1. In the art of lubrication of a controlled-slip differential which has started to slip extensively due to substantial wear, the improvement wherein the previously used lubricant is replaced by a lubricant consisting essentially of non-hydrocarbon additives and a hydrocarbon base stock having a kinematic viscosity at 210 in the range of 1.5-2000 cs. and consisting essentially of a blend of at least one C C naphthene and from 0.1-20 parts by weight, based on said naphthene of at least one member from at least one of the following groups (a) and (b):

(a) a synthetic liquid C C olefin homopolymer; and

(b) a member from group (a) above which is at least partially hydrogenated; and wherein the amount of said blend which is present in said base stock is suflicient to provide a greater coefficient of traction, measured at 600 ft./min., 200 R, 400,000 p.s.i., than would be provided by substitution of the same 211110111111. of ASTM Oil No. 3 for said blend in said base stoc 2. The improvement of Claim 1 wherein said C -C naphthene has a glass transition temperature in the range of '90 to 30 C. and contains, as a structural nucleus, a cyclohexyl hydrindan, di(cyclohexyl) alkane, adamantane, spirodecane, spiropentane, perhydrofiuorene, perhydrobiphenyl, perhydroterphenyl, decalin, norbornane, perhydroindacene, perhydrohomotetraphthene, perhydroacenaphthene, perhydrophenanthrene, perhydrocrysene, perhydroindane 1 spirocyclohexane, perhydrocarylphyllene, pinane, camphane, perhydrophenylnaphthalene or perhydropyrene.

3. The improvement of Claim 1 wherein said lubricant also contains an extreme pressure additive and an additive which lowers the static friction of said lubricant.

4. The improvement of Claim 3 wherein said extreme pressure additive consists essentially of a compound of phosphorus.

5. The improvement of Claim 4 wherein said extreme pressure additive consists essentially of tricresyl phosphate.

6. The improvement of Claim 1 wherein said naphthene comprises hydrogenated dimers and trimers of alphamethyl styrene.

7. The improvement of Claim 6 wherein said blend contains from 0.120 parts by weight, based on said naphthene, of a hydrogenated polymer of a C monoolefin.

8. The improvement of Claim 1 wherein said C -C olefin is at least one C, olefin.

9. The improvement of Claim 8 wherein said C olefin consists essentially of isobutylene.

10. The improvement of Claim 1 wherein said kinematic viscosity at 210 F is in the range of 550 cs. and wherein the channel point is at least 10 F.

11. The improvement of Claim 1 wherein in said group (b) the hydrogenation is to at least 98% saturation.

12. The improvement of Claim 1 wherein said lubricant comprises a blend of the following components in about the indicated volume proportions:

35.0% hydrogenated polybutene 52.6% hydrogenated poly (alpha-methyl styrene) 7.4% extreme pressure additive 3.0% dispersant 1.0% low static modifier 1.0% synthetic sulfurized oil and wherein the said hydrogenated components are at least 98% saturated.

13. The improvement of Claim 1 wherein said lubricant comprises limited slip axle additives and a blend of the following components in about the indicated volume proportions:

61.0 parts perhydrogenated poly (alpha-methyl styrene) 33.1 parts completely hydrogenated polyolefin oil.

14. The improvement of Claim 1 wherein said lubricant comprises in the range of 33.1-35.0 volume percent bydrogenated polybutene and 52.6-61.0 volume percent hydrogenated poly (alpha-methyl styrene).

15. The improvement of Claim 1 wherein said replacement provides increased torque at low speed dynamic conditions compared to said diiterential containing said used lubricant.

References Cited UNITED STATES PATENTS 3,010,903 11/1961 Clarke et a1 25249.9 3,211,653 10/1965 OHalloran 25250 3,410,801 11/1968 Tunkel et a1 25274 3,608,385 9/1971 Duling et al. 25273 3,394,603 7/1968 Rounds 74200 3,077,452 2/1963 Fainman 25259 3,370,010 2/ 1968 Isaacson 252-59 3,236,771 2/1966 Matson 25232.7

OTHER REFERENCES Rounds 1 our. of Chem. & Engineering Data, vol. 5, No. 4, October 1960, pp. 499-507.

Boner Gear & Transmission Lubricants (1964), p. 448.

WARREN H. CANNON, Primary Examiner US. Cl. X.R. 25249.8, 59 

1. IN THE ART OF LUBRICATION OF A CONTROLLED-SLIP DIFFERENTIAL WHICH HAS STARTED TO SLIP EXTENSIVELY DUE TO SUBSTANTIAL WEAR, THE IMPROVEMENT WHEREIN THE PREVIOUSLY USED LUBRICANT IS REPLACED BY A LUBRICANT CONSISTING ESSENTIALLY OF NON-HYDROCARBON ADDITIVES AND A HYDROCARBON BASE STOCK HAVING A KINEMATIC VISCOSITY AT 210*F. IN THE RANGE OF 1.5-200.0 CS. AND CONSISTING ESSENTIALLY OF A BLEND OF AT LEAST ONE C13-C29 NAPHTNENE AND FROM 0.1-20 PARTS BY WEIGHT, BASED ON SAID NAPHTHENE OF AT LEAST ONE MEMBER FROM AT LEAST ONE OF THE FOLLOWING GROUPS (A) AND (B): (A) A SYNTGETIC LIQUID C3-C8 OLEFIN HOMOPOLYMER; AND (B) A MEMBER FROM GROUP (A) ABOVE WHICH IS AT LEAST PARTIALLY HYDROGENATED; AND WHEREIN THE AMOUNT OF SAID BLEND WHICH IS PRESENT IN SAID BASE STOCK IS SUFFICIENT TO PROVIDE A GREATER COEFFICIENT OF TRACTION, MEASURED AT 600 FT./MIN., 200*F., 400,000 P.S.I., THAN WOULD BE PROVIDED BY SUBSTITUTION OF THE SAME AMOUNT OF ASTM OIL NO. 3 FOR SAID BLEND IN SAID BASE STOCK. 